Another name for the principle of text and graphics is multimedia. Students learn more effectively with words and graphics instead of just words. However, it is not enough to put a graphic in a presentation, the graphic must be relevant to the written words. It is important the words and pictures are on the same slide - they must be "presented simultaneously rather than successively." For text and graphics to work in a presentation, it is best to follow the less is more rule. Well placed visuals, sounds and words will aid a student's learning by eliminating unnecessary words and irrelevant visuals and audios. The effect of bad text and graphics is greater for those students who have little knowledge about the subject matter. Those who are familiar with the subject matter use their cognitive abilities to ignore the distractions caused by inferior text and graphics and too many graphics.
Reference:
Cognitive Design Solutions (n.d). Principles of Multimedia. Retrieved from: http://www.cognitivedesignsolutions.com/Media/MediaPrinciples.htm